Exemplary embodiments of the present invention relate to a driving circuit and a driving method for an electro-optical device which reduce crosstalk and display unevenness.
The related art includes electro-optical devices, such as liquid crystal display devices using liquid crystal as an electro-optical material for display units in various information processing apparatuses, for liquid crystal televisions, and for devices usable as display devices which substitute cathode ray tubes (CRTs).
Such a liquid-crystal display device, for example, includes an element substrate provided with pixel electrodes arranged in a matrix shape and switching elements, such as TFTs (Thin Film Transistors), connected to the pixel electrodes, a counter substrate on which a counter electrode which faces the pixel electrodes, is formed, and liquid crystal, which is an electro-optical material, filled between the substrates.
The TFT is turned on by a scanning signal (gate signal) which is supplied through a scanning line (gate line). When the scanning signal is applied to the switching element to turn it on, an image signal having a voltage corresponding to a gray-scale level is applied to the pixel electrode through a data line (source line). In doing so, an electric charge corresponding to the voltage of the image signal is accumulated in a liquid crystal layer between the pixel electrode and the counter electrode. After the electric charge is accumulated, even if the scanning signal is removed to turn off the TFT, the accumulated electric charge in each electrode is maintained by the capacitive characteristic of the liquid crystal layer or a storage capacitor.
When the switching element is driven and the amount of the accumulated electric charge is controlled according to the gray-scale level in such a manner, the alignment state of the liquid crystal changes for every pixel, optical transmittance changes, and brightness changes for every pixel, thereby making it possible to display the gray-scale.
In the liquid crystal device, the application of the DC component of an applied signal may cause the decomposition of the liquid crystal, contamination due to impurities in liquid-crystal cells, displayed-image sticking, and others. Therefore, in general, an inversion driving which inverts a polarity of a driving voltage for each pixel electrode, for example, at each frame of an image signal, is performed. A plane inversion driving such as a frame inversion driving is a method in that polarities of driving voltages for all pixel electrodes constituting an image display region are made identical, and thus the driving voltages are inverted at a constant interval.
With the capacitive characteristic of the liquid crystal layer and the storage capacitor being taken into account, the charge needs to be applied to the liquid crystal layer at each pixel just for a partial period. Therefore, to drive a plurality of pixels arranged in a matrix shape, it is necessary that a scanning signal be simultaneously applied to pixels connected to the same scanning line through the scanning line, image signals be supplied to the pixels through the data lines, and the scanning line to which the image signals are supplied be sequentially switched. In other words, in the liquid crystal display device, a time division multiplex driving system is allowed, in which the scanning lines and the data lines are shared by a plurality of pixels.
As described above, in the liquid crystal device, the driving voltages are applied to the pixels just for a partial period with the capacitive characteristic being taken into account. Even when the TFTs are turned off, however, the pixel electrodes are influenced by potentials on the source lines due to the effect of coupling capacitors and the leakage of the electric charge. Such a potential fluctuation on a voltage applied to pixels causes non-uniform display in a screen and image quality deterioration especially at a half tone region.
Therefore, in order to address and/or avoid such problems, an inversion driving system in which an inversion driving performed at each frame and a line inversion driving for changing the polarities of driving potentials at each line are incorporated is adapted in the liquid crystal device. Since the polarities of the image signals supplied through the source lines are switched in a relatively short time, the effects of the coupling capacitors and the leakage of the electric charge are reduced.
However, in the case of the line inversion driving system, an electric field (hereinafter, referred to as a horizontal electric field) is generated between adjacent pixel electrodes on the same substrate in the column or row direction in which voltages having different polarities are applied. Further, in a dot inversion driving system, a horizontal electric field is generated between adjacent pixel electrodes in the row or column direction in which voltages having different polarities are applied.
When such a horizontal electric field is generated between adjacent pixel electrodes, at an edge of the pixel electrode, the tilt direction of the liquid crystal molecules is affected by the horizontal electric field to disorder the alignment of the liquid crystal. Due to the alignment turbulence (disclination) of the liquid crystal molecules, a stripe shape (stripe unevenness) appears along the defective alignment portion. That is, light leakage occurs in the disclination region. Further, when the disclination region is made of a non-opened region, an aperture ratio is lowered.
Related art document Japanese Unexamined Patent Application Publication No. 5-313608 discloses a technique in which disclination due to the horizontal electric field is reduced or suppressed and uniformity of the screen is secured. In this technique, one horizontal period is divided into a first period and a second period. Specifically, in the first period, driving pulses are applied to the scanning lines and the image signals are supplied to the data lines, such that the image signals are applied to the pixel electrodes. Further, in the second period, image signals having opposite polarities to the image signals previously applied are supplied to the data lines, without supplying the driving pulses to the scanning lines.
However, in the technique disclosed in Japanese Unexamined Patent Application Publication No. 5-313608, the time to be used for writing onto the pixels is a half of the normal time. Accordingly, there is a problem in that the write time is not sufficient.